Synthesis of poly(lactic acid) by heterogeneous acid catalysis from d , l -lactic acid

Poly(lactic acid) (PLA) is an important polymer because of its significant biocompatibility and biodegradability. Supported H 3 PW 12 O 40 (H 3 PW) on activated carbon was utilized for the catalytic polymerization of D,L-lactic acid, resulting in blends of PLA. The stability of the polymer was monitored by thermogravimetry (TGA), and the decomposition temperature (T d ) was used to determine the optimal production conditions (i.e., temperature of 180 °C for 15 h; 0.1 wt. % catalyst; 20 wt. % H 3 PW/carbon calcined at 400 °C). The best catalyst was reused three times with good activity and recovery (95 %) and was analyzed to confirm the consistency of its Keggin structure, dispersion, and acidity, which are important parameters that affect the catalyst’s activity. The obtained polymer was characterized by gel permeation chromatography (GPC), Fourier-transform infrared spectroscopy (FT-IR), 1 H/ 13 C nuclear magnetic resonance (NMR) spectroscopy, specific optical rotation ([α] D 25 ), powder X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The average molar mass of the polymer was 17,400 g mol −1 . Blends of poly(lactic acid) with 85 % poly(L-lactic acid) stereospecific isomer were obtained. Graphical Abstract Stereoselective synthesis of 85 % PLLA from polymerization of d,l-lactic acid using 12-tungstophosphoric acid supported on carbon as a catalyst